Gas purification apparatuses are used to remove contaminants from gases passing through the apparatuses and in atmosphere, and air purification apparatuses are used to remove contaminants from air in a room. Air purification apparatuses can be employed as stand-alone units in a room or can be used, for instance, with respect to a room's ventilation or air-conditioning system. Gas purification apparatuses can be used with respect to electrostatic precipitators to precipitate particles from industrial gas streams. In both apparatuses, different techniques can be employed to remove contaminants from the gas. For example, mechanical filters, including Titanium dioxide coated filters can be used, as well as ultraviolet irradiation and ozone application to the gas. In addition, electronic purification techniques can also be used, such as ionisation.
Ionisation requires the generation of ions and free electrons which then attach to substances and contaminants in the gas to ionise them, and thus purify the gas. For example, in respect of an existing air purification apparatus, high voltage is used to ionise air molecules to generate ions (typically negative ions) and free electrons. In this existing air purifier, ion generation is typically provided with an annular ground electrode and a needle-like discharge electrode disposed centrally within the ground electrode. When high voltage is applied to the needle electrode, a corona discharge occurs and ions are generated from the needle electrode. The ground electrode and needle-like discharge electrode disposed centrally within the ground electrode form a plasma chamber and the region between the needle-like discharge electrode and the ground electrode is a plasma region having an electrical field.
In these existing air purifiers, the needle electrode is delicate and can easily be moved or bent when, say, cleaning the ground electrode or during transportation of the purifiers (or just over time). Cleaning is required on a regular basis due to a build-up of precipitated waste on the needle-like electrode and particularly on the ground electrode. Further, if the needle electrode is bent, the plasma region is no longer uniform and contaminants flowing in the air through the ground electrode into the plasma region can be subjected to lower electrical field intensity and less ions in the area in the region where the distance between the needle electrode and the ground electrode is greater; thus contaminants flowing through this area may not be eliminated. Further, the intensity of the resultant electrical field in the plasma region might not be adequate to cause an irreversible electroporation of microorganisms in the air and therefore cannot destroy certain microorganisms in the air. Indeed, in some existing air purifiers with multiple ones of these plasma chambers, the overall performance of the purifiers may decrease significantly due to an intensity decrease in the electric field in all the plasma chambers if just one of the needle electrodes is bent.
Another problem with these existing air purifiers is that electromagnetic interference (EMI) is generated within the plasma chambers which requires shielding using filters to reflect and absorb the EMI. These filters, however, also increase the resistance against air flow through the plasma chambers and result in an impeded air flow through the air purifiers—thus reducing the air purifiers' efficiency. Also, the increased pressure drop across these existing air purifiers may require a more powerful fan to push air through the air purifier which may also be undesirable.